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The investigators hypothesise that modification of the Atrial Fibrillation (AF) substrate by radiofrequency ablation would improve single procedure success rates for Radio Frequency Ablation (RFA) for Non-paroxysmal AF when compared to that achieved with short-term peri-procedural anti-arrhythmic drug therapy alone.

Using a 4mm irrigated tip radiofrequency ablation catheter a series of lesions >2 mm outside pulmonary vein (PV) ostia will be made to encircle and electrically isolate the pulmonary veins in two ipsilateral pairs (wide area circumferential ablation, WACA). A 20-pole PV mapping catheter will be used to confirm electrical isolation. If the patient is in atrial fibrillation at this stage, sinus rhythm would be restored with electrical cardioversion and PVI would be confirmed in sinus rhythm

Using a 4mm irrigated tip radiofrequency ablation catheter a series of lesions >2 mm outside PV ostia will be made to encircle and electrically isolate the pulmonary veins in two ipsilateral pairs (wide area circumferential ablation, WACA)34. A 20-pole PV mapping catheter will be used to confirm electrical isolation. Once PVI has been achieved, patients will go onto to receive additional linear ablation lesions. These will include a left atrial roof line, mitral isthmus line, (including ablation inside the coronary sinus if necessary), and ablation on the cavotricuspid isthmus. If the patient is in atrial fibrillation at this stage, the acute end-point would be signal obliteration at the ablated area. Once sinus rhythm is restored with electrical cardioversion, PVI would be confirmed in sinus rhythm and conduction block across the LA roof line, Mitral line and CTI will then be verified with appropriate pacing manoeuvres.

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Persistent AF: AF requiring Electrical/ Chemical cardioversion or that lasting >7 days. These patients may be in AF or in sinus Rhythm at the time of their initial assessment and/ or at the time of their ablation.

Continuous Persistent AF: These patients are persistently in AF with or without antiarrhythmic drug therapy, as confirmed on a 24 hour Holter. They may have undergone previous cardioversion(s).

Sustained Paroxysmal AF with underlying substrate: Patients with Individual AF episode(s) lasting >12 hours but less than 7 days plus one or more of the following:

Age >65 years 21

Individual AF episode(s) lasting >24 hours

Significant left atrial dilatation of >45 mm on Echo (Parasternal Long Axis view)

Inability or unwillingness to receive oral anticoagulation with warfarin

Previous Ablation procedure for AF

Unwillingness or inability to complete the required follow up arrangements

Presence of long standing persistent AF with continuous AF longer than 12 months. This includes patients in whom sinus rhythm may have been maintained following electrical cardioversion for a period of less than 1 week at a stretch.